1. Field of the Invention
The present invention relates to a magnetic coupling configured to transmit power from a drive shaft to a driven shaft, and also relates to a camera platform that uses a magnetic coupling.
2. Description of the Related Art
Generally, a magnetic coupling is capable of transmitting power of shafts in a non-contact manner by using a magnetic force acting between a magnet located at a drive shaft and a magnet located at a driven shaft. Further, the magnetic coupling has a high silencing performance in comparison with a mechanical coupling. The magnetic coupling, however, may cause a phase difference in rotation between the drive shaft and the driven shaft since the magnetic coupling transmits power in a non-contact manner. The phase difference may generate vibration in the circumferential direction at the driven shaft because the magnet located at the drive shaft and the magnet located at the driven shaft attract each other according to magnetic force that occurs between them.
According to Japanese Patent Application Laid-Open No. 07-111772, magnet portions are mounted on the drive shaft and the driven shaft respectively facing each other, wherein either one of these magnet portions includes two magnets. These two magnets are displaced in the opposite circumferential direction respectively relative to the other magnet portion. In a neutral position, the two magnets generate supporting force in the circumferential direction between the drive shaft and the driven shaft. The supporting force can reduce the occurrence of a phase difference, thus suppressing vibration occurring in the circumferential direction.
Japanese Patent Application Laid-Open No. 11-013855 discusses a detecting unit that can accurately detect displacement of a relative position between a drive shaft and a driven shaft to implement a method for performing feedback control of a source of power, such as a motor, connected to the drive shaft according to an output from the detecting unit so as to dampen vibrations occurring at the driven shaft.
Although the method discussed in Japanese Patent Application Laid-Open No. 07-111772 generates a supporting force in the circumferential direction in a neutral position and reduces the occurrence of a phase difference, it is difficult to completely prevent the occurrence of a phase difference because the magnetic coupling uses a non-contact type power transmission. It is also difficult to perform precise control, according to Japanese Patent Application Laid-Open No. 07-111772, since no method is available for damping a vibration itself occurring in the circumferential direction.
Although the method discussed in Japanese Patent Application Laid-Open No. 11-013855 enables quickly damping vibrations of the driven shaft in the circumferential direction by performing feedback control of a source of power based on an output from the detecting unit, the method requires a complex configuration to perform feedback control.